Electroless plating solutions containing sulfamic acid and salts thereof

ABSTRACT

Sulfamic acid and its salts are used to stabilize alkaline electroless copper plating solutions against decomposition. When employed in the second bath of a two-bath electroless plating system, the presence of sulfamic acid and its salts permits rapid deposition, over a broad range of concentrations, of copper onto an initial copper or nickel plate, while preventing deposition of copper onto a noble metal catalyzed surface. The stabilizers also serve to supplement single-bath electroless copper plating systems.

Elited States Patent [1 1 Kadison et al.

[ ELECTROLESS PLATING SOLUTIONS CONTAINING SULFAMIC ACID AND SALTSTHEREOF [75] Inventors: Leon A. Kadison; Eileen Maguire,

both of Pasadena, Calif.

[73] Assignee: Crown City Plating Company, El

Monte, Calif.

[22] Filed: Sept. 6, 1972 [2]] Appl. No.: 286,837

Related US. Application Data [63] Continuation-impart of Ser. No.118,480, Feb. 24,

1971, abandoned.

[52] US. Cl. 106/1, 117/47 A, 117/130 E [51] Int. Cl. C23c 3/02 [58]Field of Search 106/1; 117/47 A,

[111 3,754,940 [451 Aug. 28, 1973 Primary Examinerl.orenzo B. HayesAttorney-Robert L. Parker, John P. Grinnell et a1.

[57] ABSTRACT Sulfamic acid and its salts are used to stabilize alkalineelectroless copper plating solutions against decomposition. Whenemployed in the second bath of a two-bath electroless plating system,the presence of sulfamic acid and its salts permits rapid deposition,over a broad range of concentrations, of copper onto an initial copperor nickel plate, while preventing deposition of copper onto a noblemetal catalyzed surface. The stabilizers also serve to supplementsingle-bath electroless copper plating systems.

5 Claims, No Drawings ELECTROLESS PLATING SOLUTIONS CONTAINING SULFAMICACID AND SALTS THEREOF This is a continuation-in-part of our applicationSer. No. 118,480, filed Feb. 24, 1971, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to theelectroless plating of resin surfaces and, more particularly, toinhibiting an electroless copper plating bath against solutiondecomposition due to impurities.

Considerable demand has developed for metal plated non-conductivearticles, particularly plastic articles. In the finished product, thedesirable characteristics of both the plastic and the metal are combinedto offer thereby the technical and aesthetic advantages of each.

Although most resins are electrically nonconductive, a metal bond to thesurface of the resin can be established by an initial plating operationknown as electroless plating. This is typically accomplished byconditioning the surface of the resin for plating by contact with astrong oxidizing acid, seeding the conditioned surface by contact with anoble metal salt, e.g., a palladium chloride solution, then immersingthe seeded surface in an auto-catalytic electroless plating solutionwherein an initial coating of a conductive metal is established bychemical deposition. The metal coating formed acts as a buss and allowsa thicker metal coating to be built up electrolytically. For mostresins, contact with the oxidizing acid is often preceded by a chemicaletch to improve the bond strength of the plate.

A typical formulation for an electroless plating solution consistsessentially of a soluble cupric salt, such as copper sulfate; acomplexing agent for the cupric ion, such as Rochelle salt; an alkalihydroxide for adjusting pH; a carbonate radical as a buffer; and areducing agent for the cupric ion such as formaldehyde.

The mechanism by which polymeric objects having surfaces catalyzed bypalladium metal may be plated auto-catalytically has been well describedin the literature, such as, for example, U.S. Pat. No. 2,874,052.

Electroless plating solutions as described above are, however, subjectto decomposition. For copper plating solutions, for example, the cupricion inherently tends to reduce to the insoluble cuprous form. This maybe overcome, in part, by the use of stabilizers, or by air agitationwhich serves to oxidize cuprous ion back to the cupric state.

Secondary sources of contamination, however, also materially contributeto decomposition. When the catalyzed plastic article is withdrawn fromthe noble metal salt bath, it too often carries with it, as drag-out,substances including copper, nickel, iron, palladium, gold, silver andeven dust particles, which are catalytic toward solution decomposition.Palladium ion (Pd is notorious in that if stainless steel tanks orequipment are in contact with electroless (copper) bath even a minuteamount of palladium ion with initiate plating of the copper onto steel.In addition, concentrations as low as one part per million will causespontaneous decomposition of the solution with attendant precipitationand loss of copper.

It has been proposed to use plastic tanks for electroless plating bathsto avoid the problem of plating on the stainless stell tanks. Even inplastic lined tanks, however, inevitable scratches in the lining resultin initiation of decomposition because the scratches provide recesseswithin which hydrogen produced during the plating reaction isconcentrated.

Attempts have also been made to stabilize electroless plating baths tominimize decomposition. However, most compounds which have been proposedas stabilizers retard the rate of electroless plating. While heating maybe employed to increase the rate of deposition, it has not beengenerally used because heating also promotes decomposition.

We have employed an alternate route to minimize loss of valuablechemicals through decomposition of the plating solutions. This involvesthe use of two plating baths. One is a strike bath in which a noblemetal catalyzed surface is initially plated in a bath essentially freeof inhibitors or inhibited only to a minor extent. The other is aplating bath in which the article with a thin deposit of plating metalis further electrolessly plated and which is inhibited by a cyanide tothe extent that if the article having the catalytic noble metal surfacewere passed directly into the bath without first passing through thestrike bath, no plating metal would be deposited on the article. In thissystem, the plating bath remains stable for extended periods of timewhile the strike bath continuously decomposes. Since the volume of thestrike bath is low relative to the volume in the plating bath, losseshave been minimized. The cyanide inhibitor, however, retards depositionrate as its concentration increases.

' SUMMARY OF T HE INVENTION It has now been found that sulfamic acid andthe salts thereof serve as unusually effective stabilizers for alkalineelectroless copper plating solutions.

They are preferably employed in the second or plating bath of a two-bathelectroless plating system. In that bath the presence of sulfamic acidand/or its salts may at molar concentrations as low as 0.02 mol perliter of solution inhibit the solution to prevent decomposition whilepreventing deposition of copper onto a noble metal catalyzed surface,but permitting rapid deposition of copper onto an article having aninitially deposited coat of a plating metal.

In addition, sulfamic acid and/or its salts may be employed along or inconjunction with other inhibitors to stabilize the strike" bath oftwo-bath electroless plat ing systems, as well as conventional alkalineelectroless copper or nickel solutions against spontaneous breakdown dueto the presence of contaminants such as noble metal ions withoutmaterially reducing plating rate onto a noble metal catalyzed surface.

DESCRIPTION The present invention relates to the use of sulfamic acidand its salts as stabilizers for electroless plating solutions,particularly as stabilizers for the second or plating" bath of atwo-bath electroless plating system. They may be employed alone or inconjunction with other known stabilizers.

Sulfamic acid is a white crystalline solid, having the formulaHSO,NI-I,, which may be converted to its cor responding salt by reactionwith a base, a metal salt, or an amine to form a compound having theformula X(SO,NI-I,)n wherein X is the cation contributed by the base,metal salt, or amine, and n is valence of the cation. The cation, ofcourse, must not have a deleterious effect upon the formulatedelectroless plating solution.

In addition to the ammonium and amine cations, such asdiethylenetriamine and diethanolamine, there may be employed as themetallic cations for the sulfamic acid salts, metals selected fromGroups Ia, Ila, Ilb, IIIb, Va, Vla, and the third period of Group VIIIof the periodic table as defined by Mendeleeff and published as thePeriodic Chart of the Atoms, by W. N. Welch Manufacturing Company.

While no wise limiting, the preferred metals are lithium, sodium,potassium, barium, nickel, zinc, magnesium, calcium, strontium,vanadium, chromium in the trivalent state, molybdenum, tungsten,cadmium, mercury, aluminum, cobalt, and copper.

The metals to be specifically avoided are lead and the noble metals, asthey are considered poisons in electroless plating solutions as well asother metals which may be considered contaminants in the solution.

The salts of sulfamic acid may be prepared by neutralization with ametal or ammonium hydroxide, as well as by direct reaction with an amineor a salt of the metal cation.

Although finding broad utility as a stabilizer for electroless platingsolutions, sulfamic acid and its salts are of particular utility asstabilizers for alkaline electroless copper plating bath of a two-bathelectroless plating system.

The two-bath system is most commonly based on a copper or nickel strikebath where an initial plate of metal is deposited, followed by immersionof the article in an alkaline electroless copper plating bath where aplate of copper is built up.

Formulations which are particularly useful as an alkaline copper basedplating bath of a two-stage electroless plating system lie within thefollowing ranges:

Alkali Hydroxide l1 14 Water to pH of Suffioient to make 1 liter Thepreferred concentration of sulfamic acid and/or its salts in the platingsolution is from about 0.3 to 4.5 mols per liter.

' As the water soluble cupric salt there may be employed copper sulfate,cupric halides, cupric nitrates, cupric acetates, and other inorganicand organic cupric salts. Copper sulfate and cupric chloride arepreferred.

As complexing agents for the cupric ion there may be employed Rochellesalts, the mono-, di-, tri-, and tetrasodium salts ofethylenediaminetetracetic acid; the ethanolamines, such astriethanolamine; nitrilotriacetic acid and its alkali metal salts;gluconic acid; gluconates; glucono- -y -lactone; N-hydroxyethyleneethylenediaminetriacetate; hydroxyalkyl substituted dialkylenetriamines, such as pentahydroxypropyl diethylenetriamine; thesalicilates; citrates; lactones, and other complexing agents well knownin the art.

As reducing agents there may be employed formaldehyde and its precursorsor derivatives such as paraformaldehyde; glyoxyl; borohydrides, such asalkali metal borohydrides and substituted alkali metal borohydrides andthe like. Formaldehyde is particularly preferred.

There may also be employed buffering agents such as sodium bicarbonate.

It will be appreciated from the above formulations that, if sulfamicacid is added directly, it will, in substance, be converted to anionized alkali metal salt as a consequence of the presence of the alkalihydroxide for pH control.

Plating solutions corresponding to the above formulations will inhibitagainst the plating of copper on a surface catalyzed with a noble metal,but will perm-it deposition onto a previously plated surface as producedin the strike bath hereinafter described.

The above plating solutions are capable of building an initial metalplate to a level sufficient to act as a buss for electroplating within 5to 10 minutes at temperatures of about 105F. The solutions are,moreover, useful over a temperature range from about F to about 150F,preferably from about F to about F.

As indicated, when the sulfamic acid solutions of this invention areused as the plating bath of a two-stage operation, the resin articles tobe plated are provided with an initial plate in a strike bath which iseither free of inhibitors or only inhibited to an extent such thatplating onto a surface catalyzed with a noble metal will not beprecluded. The strike baths employed are generally those capable ofdepositing an initial coat of metal onto the surface of a noble metalcatalyzed article within three minutes are room temperature.

The compositions used in the strikebath may be any of thoseconventionally employed for electroless deposition of plating metal on anonconductive article. Any conventional electroless copper platingsolution may, for instance, be used as a room temperature strike bath.Formulations for an electroless copper strike bath include, for example,the following compounds in aqueous solution within the ranges set forthbelow:

Ingredient Molar Concentration Soluble Cupric Salt 0.02 0.15 ComplexingAgent 0.03 0.75 Reducing Agent 0.05 1.50 pH Adjustor sufficient to givepH (alkali hydroxide) from 12 to 14 The nature of the soluble cupricsalts, complexing agents, and reducing agents which may be used are thesame as those employed in the plating bath as set forth above.

Since only a thin film of copper is deposited in the strike bath, itsvolume can be small, as that the solution can be economicallyreplenished or discarded as decomposition occurs. For this reason, thestrike bath can be operated without any inhibitor or a small amount ofinhibitor for which sulfamic acid and its salts may serve as all or partof the inhibitor system.

Similar solutions are employed when it is desired to deposit an initialnickel plate except that there is employed a soluble nickel salt.

For convenience, the detail of the use of the sulfamic stabilizedplating solution of the present invention will be made with reference toelectroless copper plating of acrylonitrile-butadiene-styrene, referredto below as ABS plastic with copper. The conditioning and activation ofthe plastic are described in general, as these steps are not, as such, apart of the invention.

A molded ABS plastic part is cleaned, pre-etched with an organicchemical solvent, if required, and then etched in an etching chemicalbath such as a mixture of chromic and sulfuric acids. After cleaning ofthe etched article, including rinsing in an alkaline cleaner, thearticle is sensitized in a stannous chloridehydrochloric acid bath andthen activated in a bath of a noble salt, such as palladium chloride, toprovide a catalytic noble metal on the surface of the plastic. Followingrinsing to remove excess palladium from the surface of the article, itis passed into the strike bath.

The strike bath can be any conventional electroless plating solution.For copper plating the preferred solutions have the followingformulation:

ingredient Concentration Rochelle Salt 34 grams/liter Caustic Soda l2grams/liter Copper Sulfate 7 grams/liter Sodium Carbonate 6 grams/literFormaldehyde ccs./liter Water Sufficient to make 1 liter The strike"bath is typically maintained at room temperature. The plastic articlewith palladium metal on its surface is immersed in the strike bath forfrom about seconds to about 3 minutes and then re moved. This is asufficient period of immersion to enable deposition of a thin copperfilm over the entire surface of the article. The strike bath, inaddition to preparing the article for deposition in the electrolessplating" bath, also serves as a collector for the bulk of thecontaminants which otherwise would pass directly into the plating bath.

Upon removal from the strike bath, the plastic article having a thincopper deposit is passed directly into the sulfamic acid stabilizedalkaline electroless copper plating bath.

The plastic article is retained in the alkaline electroless plating bathfor a period of from 5 to 10, preferably 3 to 6 minutes. During thisperiod of time, additional thicknesses of copper sufi'icient to permitsubsequent electrolytic metallic plating are deposited. After removalfrom the electroless plating bath, the article is rinsed and soaked and,if electrolytic plating is required, is passed to the electroplatingprocess.

While sulfamic acid and its salts are particularly useful as stabilizersfor the above described two-step electroless plating processes, they arealso useful as stabilizers for one-step electroless nickel platingprocesses and as the sole or as supplemental stabilizers for single-bathelectroless copper plating processes.

When used as a stabilizer or inhibitor for single-bath electrolesscopper plating solutions, sulfamic acid and- /or its salts may beemployed, depending on the plating potential of the bath, in an amountup to about 0.5 mol per liter. Plating potential of a bath is dependent,in general, on the concentration of reducing agent and alkali metalhydroxide. At a higher end of the concentrations set forth above,sulfamic acid may be added as a stabilizer without causing the bath tobecome a plating bath, that is, one incapable of depositing copper ontoa noble metal catalyzed surface.

As plating potential goes down, however, at a constant concentration ofsulfamic acid and/or its salts, the bath will, at some concentration ofreducing agent and alkali metal hydroxide, become a plating bath.

The test to determine this is, however, simple, requiring only immersionof a noble metal catalyzed article into a formulated solution todetermine if plating will occur onto its surface. If so, then thesolution is functional as a strike bath or single-bath alkaline copperplating solution. If a deposit of copper does not occur, then thesolution is functional as a plating bath for a two-bath plating system.

EXAMPLES l to 5 Several plating solutions were formulated containingvarying amounts of copper sulfate and sulfamic acid as the stabilizer.As a control, there was formulated a solution without a stabilizer. Thesolutions are shown in Table I.

TABLE I Component (mols/liter) 1 2 3 4 5 Control Copper sulfate 0.0360.036 O. 036 0. 036 0.036 0.036 Rochelle Salt. 0. 14 0. 14 0. 14 0. 140. 14 0. l4 Formaldehyde H 0 11 0. 027 0. 027 O. 1. 30 0. 11 Sodiumbicarbonate 0. 11 0. 11 0. 11 0. 11 0. 11 Sulfamic acid 0. 51 0. 022 0.037 2. 2 4. 35 Sodium hydroxide, total 0. 88 0.392 0. 407 2. 96 5. 39 0.37 Free sodium hydroxide 0. 125 0. 125 0.125 0.51 0. 79 0. 125

In each instance, the balance of the solution was an amount of watersufficient to make one liter.

With respect to solutions 1 to 5 after immersing ABS resin articleshaving a noble metal catalyzed surfaces in the baths maintained at 105Ffor 15 minutes, no perceptible copper deposit was visible upon removal.

When articles which had been provided with an initial plate of copper ina strike bath were immersed, a film of copper sumcient to act as a bussfor electrolytic plating was deposited within 5 to 10 minutes.

Samples of the solutions were then used as plating baths for 5 minutesand then allowed to stand for 12 hours. No perceptible decomposition wasobserved.

For the control, the solution was used as a plating bath for a catalyzedresin surface for 5 minutes at 105F and then allowed to stand. Itdecomposed with attendant precipitation of copper within 30 minutes.

Example 6 There was employed as a plating bath a solution of thefollowing composition.

Component Amount Versene" 100' 40.0 cc. CuSO -5H,O 9.5 gr. SodiumSulfamate 65.0 gr. Sodium Hydroxide 9.0 gr. Sodium Bicarbonate 9.3 gr.Formalin 9.0 cc. Free Sodium Hydroxide 5.0 gr. Water Sufficient to make1 liter 1. An about 40% aqueous solution of the tetrasodium salt ofethylenediaminetetracetic acid manufactured by the Dow ChemicalCorporation.

2. A salt prepared by neutralizing sulfamic acid with sodium hydroxide.3. A 38% solution of formaldehyde in water.

While maintaining the bath at l05F, a molded ABS plaque suitably etched,sensitized by immersion in a stannous chloride-hydrochloric acid bathand activated in a palladium chloride bath, was immersed for 5 minutes.No deposition of copper onto the plaque occurred.

However, when a plaque an initial strike" coat of copper was immersed inthe bath, there was continued an electroless deposit of copper onto theplaque.

EXAMPLE 7 In this example the electroless plating bath had the followingcomposition:

Triethanolamine 10 cc. CuSO -5H O 9.5 gr. Sodium sulfamate 24.5 gr.Formalin 10.0 cc. Sodium Bicarbonate 6.0 gr. 50% Aqueous Caustic Soda l1.0 cc. Water 1 Sufficient to make 1 liter With the bath maintained at atemperature of 1 F the plating procedure of Example 6 was repeated.Identical results were obtained.

EXAMPLE 8 In this example the stabilizer for the electroless platingbath was made by forming an aqueous solution of 5 grams of sulfamic acidand 3.5 cc. diethylenetriamine. The resultant aqueous solution of thediethylenetriamine-sulfamic acid salt had a pH of 7.5. The balance ofthe plating bath was as follows:

50% aqueous solution of NaOH 19.4 cc. Sodium bicarbonate 9.3 gr.Rochelle salt 40.0 gr. CuSO,-5H,O 9.5 gr. Formalin 10.0 cc. WaterSufficient to make 1 liter In preparing the bath the sodium hydroxide,sodium bicarbonate and Rochelle salt were dissolved in water and addedto the solution of diethylenetriamine and sulfamic acid prior to theaddition of the cupric sulfate, which was also dissolved in water, andFormalin to the resulting mixture. While maintaining the bath at atemperature of 100F the plating procedure described in Example 6 wasrepeated. The results were identical in that no plating occurred on thenoble metal catalysed surface but plating occurred on plaque having aninitial deposit of copper as provided by a strike bath.

EXAMPLE 9 The plating solution employed was identical to that describedin Example 8 except that the stabilizer was a diethanolamine salt ofsulfamic acid. The stabilizer was prepared by dissolving 10 grams ofsulfamic acid and 1 1.5 cc. of diethanolamine in water. The resultantaqueous mixture of the salt has a pH of 7.5.

While maintaining the bath at ambient temperature the plating operationof Example 6 was repeated. Identical results were obtained.

EXAMPLE 10 A stabilizer for a plating solution was prepared bydissolving grams of sulfamic acid and 20.34 grams of barium carbonate inwater and agiting the mixture until all signs of reaction ceased. To thebarium sulfanate solution there was added the following ingredients.

Versene' 100 85 cc 50% aqueous solution of NaOH [0 cc Rochelle salt 40gr. CuCl,-2H,O 6.48 gr. Formalin 10.0 cc Water sufficient to make 1liter The resultant plating bath had a free sodium hydroxide content of6.6 gr./l. While maintaining the bath at 105F, the plating proceduredescribed in Example 6 was repeated. Identical results were obtained.

EXAMPLE 1 l Nickel sulfamate was prepared by dissolving 15.27 gramsnickel carbonate and 25 grams sulfamic acid in water. The mixture wasagitated until all signs of reaction ceased. The solution of nickelsulfamate was the stabilizer for a plating bath, the balance of whichwas formulated from the following components:

Versene" 100 115 cc 50% aqueous solution of NaOH 6.75 cc CuSOrSl-bO 9.5gr. Formalin 10 cc water Sufficient to make 1 liter When the solutionwas employed at room temperature and plating procedure of Example 6 wasrepeated, identical results were obtained.

Example 12 To 20 grams of sulfamic acid dissolved in 100 cc water therewas added 27.4 grams lead carbonate. The resulting mixture was stirreduntil all reaction ceased. 29.64 grams of zinc sulfate was then added tothe mixture. After permitting the mixture to stand for 1 hour there wasformed a precipitable of lead sulfate which was filtered from thesolution. The filtrate consisting of an aqueous solution of zincsulfamate and having a theoretical zinc sulfamate content of 26.75 gramswas used as the stabilizer in a plating solution of the followingadditional constituents:

Versene I00 cc 50% aqueous solution of NaOH 19.4 cc Sodium bicarbonate9.3

Rochelle salt 97.0 gr CuSO -5H,O 9.5 gr Fonnalin 10 cc Water Sufficentto make 1 liter The resultant bath had a free caustic content of 5 gramsper liter. While maintaining the bath at F the plating proceduredescribed in Example 6 was repeated. Identical results were obtained.

EXAMPLE 13 An aqueous alkaline copper solution containing 7.5 grams perliter CuSO '5l-1 O, 28 grams per liter Rochelle salt, 9.5 grams perliter sodium carbonate 12 grams per liter free sodium hydroxide, 10grams per liter of the sodium salt of sulfamic acid and 26 cc per literFormalin was prepared.

Two plaques molded from Cycoloc" EP-35l0,-a plating grade of ABS resinmanufactured and sold by the Marbon Division of Borg-Warner Corporationwere subjected to an etch in a chromic acid solution and then immersedin a catalyst solution containing colloidal palladium, known as Cuposit'9-F and then into Cuposit'" Accelerator 19, both manufactured by theShipley Company and disclosed in U.S. Pat. No. 3,011,290 to form an ABSsubstrate which would accept an electroless copper deposit.

Following activation the plaques were rinsed in deionized water toremove any residue of catalyst and accelerator solutions from thesurface.

The plaques were immersed into the aqueous alkaline copper solution for10 minutes. A uniform plate of copper was deposited. After plating bothplaques, the bath was allowed to remain overnight with continualagitation. After that period of time no solution decomposition wasobserved.

EXAMPLE 14 There was prepared an electroless copper bath of thefollowing composition:

CuSO -SI-I,O 9.5 gr. 50% aqueous solution of NaOI-I 26.0 cc Sodiumbicarbonate 9.3 gr. Rochelle salt 39.0 gr. Sodium Sulfamate 36.8 gr.Formalin 20.0 cc Water Sufficient to make 1 liter EXAMPLE 15 There wasprepared an aqueous electroless nickel strike solution of the followingcomposition: NiCl -6H O 12 gr./l; citric acid 16 gr./l; ammoniumhydroxide 15 cell; ammonium carbonate 25 gr/l; diethanolamine l cc./l;hydrated sodium hypophosphite 20 gr./l, the balance being water.Solution pH was 8.5.

A plaque catalyzed in the manner described in Example 13 was immersed inthe bath which was maintained at a temperature of 105F for 1.5 minutes.There was deposited an initial electroless nickel plate. The plaque wasremoved from the bath, rinsed and immersed in a plating solution havingthe following composition: CuSO '5H,O 9.5 gr./l; sodium bicarbonate 9.4gr./l; Rochelle Salt 39.0 gr./l; free sodium hydroxide 5.0 gr./1;formaldehyde (Formalin) 8 cc./ 1 and the sodium salt of sulfamic acid toprovide sulfamic acid in an amount equivalent to 50 gr./l, the balanceof the solution being water.

Immersion in the plating solution" was for minutes at a solutiontemperature of l05F.

A plate of copper deposited on the initial nickel plate.

EXAMPLE 16,

The procedure of Example 15 was repeated except there was used as thestrike solution the solution described in' Example 13. Immersion was 2minutes at ambient temperature. In addition the plaque was not rinsedafter removal from the strike"bath. Following removal from the strikebath, the plaquewas immersed in the plating" solution described inExample l5. After 10 minutes a plate of copper sufficient to act as abus for electrolytic plating was deposited.

What is claimed is: e

1. In an aqueous alkaline electroless copper plating solution capable ofdepositing a plate of copper onto a noble metal catalyzed surface andcontaining at least one water soluble cupric salt, at least onecomplexing agent for cupric ions, at least one reducing agent for cupricions and a pH adjuster tomaintain the solution alkaline, the improvementcomprising an inhibitor system to prevent spontaneous decomposition ofsaid solution in the presence of at least catalytic noble metal ionssaid inhibitor system containing up to about 0.5 mole per liter ofsolution of a sulfamic acid compound selected from the group consistingof sulfamic acid, salts of sulfamic acid and mixtures thereof.

2. In an aqueous alkaline electroless copper plating solution comprisingat least one water soluble cupric salt, at least one complexing agentfor cupric ions, at least one reducing agent for cupric ions and a pHadjustor to maintain the solution at a pH of about 1 l to 14, theimprovement comprising a sulfamic acid compound selected from the groupconsisting of sulfamic acid, salts of sulfamic acid and mixtures thereofsaid sulfamic acid compound being present in an amount from about 0.02to about 4.5 moles per liter of solution and sufficient to preventdeposition of copper on an article having a catalytic noble metalsurface but in sufficient to prevent deposition of copper onto anarticle having a thin coating of a deposited metal receptive tothedeposition of copper from said solution.

3. An aqueous alkaline electroless copper plating solution as claimed inclaim 2 in which the sulfamic acid compound concentration is from about0.3 to about 4.5 mols per liter of solution. 1

4. An aqueous alkaline electroless copper plating solution which willprevent copper deposition onto a noble metal catalyzed surface but willnot prevent copper deposition onto a metal plate receptive to thedeposition of copper from said solution, the solution comprising fromabout 0.2 to about 0.15 mols per liter of a water soluble ionic cupricsalt; from a 0.03 to about 0.75 mols per liter of a complexing agent forcupric ions; from about 0.025 to 0.5 mols per liter of a reducing agentfor cupric ions; an amount of an alkali metal hydroxide to maintain thesolution at a pH of from about II to about 14.0 and from about 0.02 toabout 4.5 mols per. liter of a sulfamic acid compound selected from thegroup consisting of sulfamic acid, salts of sulfamic acid and mixturesthereof.

5. An aqueous alkaline electroless plating solution as claimed in claim4 in which the sulfamic acid commols per liter of solution.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0.3.754.940 Dated Angst 28, 1973 Invent (s) LEON A. KADISON and EILEENMAGUIRE It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column Column Column Column Column Column Column Column Column (SEALAttes EDWARD M. FLETCHER, JR Atte sting Officer line line , line line ,line line 9, line line 28 "are" should read at 49, "as" should read so Q51, "Formalin should read. Formalin l6 "tge" should read the l7,"suface" should read surface 10, line 27, "in suffi-" should readinsuffi- Signed and sealed this 19th day of February 19714..

C. MARSHALL DANN Commissioner of Patents

2. In an aqueous alkaline electroless copper plating solution comprisingat least one water soluble cupric salt, at least one complexing agentfor cupric ions, at least one reducing agent for cupric ions and a pHadjustor to maintain the solution at a pH of about 11 to 14, theimprovement comprising a sulfamic acid compound selected from the groupconsisting of sulfamic acid, salts of sulfamic acid and mixtures thereofsaid sulfamic acid compound being present in an amount from about 0.02to about 4.5 moles per liter of solution and sufficient to preventdeposition of copper on an article having a catalytic noble metalsurface but in sufficient to prevent deposition of copper onto anarticle having a thin coating of a deposited metal receptive to thedeposition of copper from said solution.
 3. An aqueous alkalineelectroless copper plating solution as claimed in claim 2 in which thesulfamic acid compound concentration is from about 0.3 to about 4.5 molsper liter of solution.
 4. An aqueous alkaline electroless copper platingsolution which will prevent copper deposition onto a noble metalcatalyzed surface but will not prevent copper deposition onto a metalplate receptive to the deposition of copper from said solution, thesolution comprising from about 0.2 to about 0.15 mols per liter of awater soluble ionic cupric salt; from a 0.03 to about 0.75 mols perliter of a complexing agent for cupric ions; from about 0.025 to 0.5mols per liter of a reducing agent for cupric ions; an amount of analkali metal hydroxide to maintain the solution at a pH of from about 11to about 14.0 and from about 0.02 to about 4.5 mols per liter of asulfamic acid compound selected from the group consisting of sulfamicacid, salts of sulfamic acid and mixtures thereof.
 5. An aqueousalkaline electroless plating solution as claimed in claim 4 in which thesulfamic acid compound concentration is from about 0.3 to about 4.5 molsper liter of solution.